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Winding of π∂su\pi\partial_s uπ∂s​u along one circle versus in cylindrical coordinates at ∞\infty∞

Proved
FiniteEnergyPlane.hasLoopWind_cylInf_of_hasLoopWind_circle

by Mazecto · Nov 4, 2026 · Mathlib 0df444a (Lean v4.33.1)

pseudoholomorphic-curvesreeb-dynamicssymplectizationwinding-numbers

Let S=H−1(1)⊂R4S=H^{-1}(1)\subset\mathbb{R}^4S=H−1(1)⊂R4 be a strictly star-shaped level, JJJ a dλ0d\lambda_0dλ0​-compatible complex structure on ξ\xiξ, and J~\tilde JJ~ the induced almost complex structure on R4∖{0}≅R×S\mathbb{R}^4\setminus\{0\}\cong\mathbb{R}\times SR4∖{0}≅R×S. Let U⊂CU\subset\mathbb{C}U⊂C be open, uuu smooth, nonvanishing and J~\tilde JJ~-holomorphic on UUU, and s∈Rs\in\mathbb{R}s∈R such that the circle ∣z∣=e2πs|z|=e^{2\pi s}∣z∣=e2πs lies in UUU. Suppose that the ξ\xiξ-component π ∂su\pi\,\partial_s uπ∂s​u, read in Hryniewicz's global frame of ξ\xiξ, has winding number kkk along t↦e2πse2πitt\mapsto e^{2\pi s}e^{2\pi it}t↦e2πse2πit. Then the loop t↦π∂sw(s,t)t\mapsto\pi\partial_s w(s,t)t↦π∂s​w(s,t) of w=pr∘u∘cylInfw=\mathrm{pr}\circ u\circ\mathrm{cylInf}w=pr∘u∘cylInf, in the cylindrical coordinates (s,t)↦e2π(s+it)(s,t)\mapsto e^{2\pi(s+it)}(s,t)↦e2π(s+it) at ∞\infty∞, has winding number k+1k+1k+1 in the same frame.

This compares the two natural loops attached to a single circle: the section read in the plane coordinate zzz and the same section read in cylindrical coordinates. It holds at each individual radius, with no condition on the other circles.

Formalization Note R4\mathbb{R}^4R4 is V 1, J~\tilde JJ~ is Jtilde H J, and π∂su\pi\partial_s uπ∂s​u in the global frame is piDs H u : ℂ → ℂ. The circle is ccwLoop (Real.exp (2 * π * s)) t. The hypothesis HasLoopWind includes that piDs H u has no zero on the circle. No energy bound or asymptotic hypothesis is assumed.

Preamble
import Definitions.Def_FiniteEnergyPlane_Winding
Formal statement
namespace FiniteEnergyPlane

open MeasureTheory Metric Filter Topology
open scoped ContDiff ENNReal Real

/-- Let `u` be smooth, nonvanishing and `J̃`-holomorphic on an open set `U` containing the circle
of radius `e^{2π s}`. If `π ∂ₛu` (in the global frame, `piDs H u`) has winding number `k` along
that circle, then the loop `t ↦ π ∂ₛw(s, t)` in the cylindrical coordinates `cylInf` has winding
number `k + 1`. -/
theorem hasLoopWind_cylInf_of_hasLoopWind_circle (H : V 1 → ℝ) (hH : IsStrictlyStarShapedLevel H)
    (J : V 1 → V 1 →L[ℝ] V 1) (hJ : IsCompatibleXiStructure H J) (U : Set ℂ) (hU : IsOpen U)
    (u : ℂ → V 1) (hu : ContDiffOn ℝ ∞ u U) (hu0 : ∀ z ∈ U, u z ≠ 0)
    (hhol : JHolomorphic.IsJHolomorphicOn (Jtilde H J) U u) (s : ℝ)
    (hmem : ∀ t, ccwLoop (Real.exp (2 * π * s)) t ∈ U) (k : ℤ)
    (hk : HasLoopWind (fun t => piDs H u (ccwLoop (Real.exp (2 * π * s)) t)) k) :
    HasLoopWind (fun t => xiCoordC H (endW H u cylInf (s, t))
      (piXi H (endW H u cylInf (s, t)) (fderiv ℝ (endW H u cylInf) (s, t) (1, 0)))) (k + 1) := by
  sorry

end FiniteEnergyPlane
Source
U. Hryniewicz, Trans. AMS 364 (2012), arXiv:1105.2077, Section 4.6; H. Hofer, K. Wysocki, E. Zehnder, GAFA 5 (1995)

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